Showerhead electrode assembly for plasma processing apparatuses

ABSTRACT

A showerhead electrode assembly of a plasma processing apparatus includes a thermal control plate attached to a showerhead electrode, and a top plate attached to the thermal control plate. At least one thermal bridge is provided between opposed surfaces of the thermal control plate and the top plate to allow electrical and thermal conduction between the thermal control plate and top plate. A lubricating material between the thermal bridge and the top plate minimizes galling of opposed metal surfaces due to differential thermal expansion between the top plate and thermal control plate. A heater supported by the thermal control plate cooperates with the temperature controlled top plate to maintain the showerhead electrode at a desired temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 10/743,062 entitled SHOWERHEAD ELECTRODE ASSEMBLY FOR PLASMAPROCESSING APPARATUSES, filed on Dec. 23, 2003 now U.S. Pat. No.7,645,341, the entire content of which is hereby incorporated byreference.

BACKGROUND

Plasma processing apparatuses are used to process substrates bytechniques including etching, physical vapor deposition (PVD), chemicalvapor deposition (CVD), ion implantation, and resist removal. One typeof plasma processing apparatus used in plasma processing includes areaction chamber containing upper and bottom electrodes. An electricfield is established between the electrodes to excite a process gas intothe plasma state to process substrates in the reaction chamber.

SUMMARY

A showerhead electrode assembly of a semiconductor substrate processingapparatus, and a thermal control plate for supporting a showerheadelectrode in a semiconductor substrate processing chamber are provided.

A preferred embodiment of a thermal control plate for supporting ashowerhead electrode in a semiconductor substrate processing chambercomprises a metal outer portion removably attachable to atemperature-controlled top plate; and a metal inner portion removablyattachable to the showerhead electrode and the top plate. The innerportion of the thermal control plate provides a thermal and electricalpath between the top plate and showerhead electrode.

A preferred embodiment of the showerhead electrode assembly for a plasmaprocessing apparatus comprises a top plate, a showerhead electrode, anda thermal control plate. The thermal control plate is attached to theshowerhead electrode and the top plate such that a central portion ofthe thermal control plate is movable relative to the top plate. At leastone thermal bridge is provided between the central portion of thethermal control plate and the top plate. The thermal bridge provides athermal and electrical path between the showerhead electrode and the topplate.

The thermal bridge preferably includes a lubricating material to permitsliding, as well as provide thermal and electrical conduction, betweenopposed surfaces of the thermal control plate and the top plate.

Another preferred embodiment provides a method of processing asemiconductor substrate in a semiconductor substrate processing chamber,which comprises (a) placing a substrate on a substrate support, whichincludes a bottom electrode, in a plasma chamber of a semiconductorsubstrate processing apparatus; (b) supplying a process gas into theplasma chamber with a showerhead electrode assembly according to apreferred embodiment; (c) generating a plasma from the process gas inthe plasma chamber between the showerhead electrode assembly and thesubstrate; (d) processing the substrate with the plasma; (e) terminatingthe generation of the plasma; and (f) removing the substrate from theplasma chamber. The showerhead electrode assembly preferably comprises aheater. In another preferred embodiment, the method comprises activatingthe heater after (e) to apply heat to the showerhead electrode tomaintain the showerhead electrode at a desired temperature, and/oractivating the heater to apply heat to the showerhead electrode during(a) to (f).

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 illustrates a portion of a preferred embodiment of a showerheadelectrode assembly and a substrate support for a plasma processingapparatus.

FIG. 2 is a top perspective view of a preferred embodiment of ashowerhead electrode assembly without the top plate.

FIG. 3 illustrates an exemplary electrical connection between a powersupply and a heater of the showerhead electrode assembly.

DETAILED DESCRIPTION

FIG. 1 illustrates a preferred embodiment of a showerhead electrodeassembly 10 for a plasma processing apparatus in which semiconductorsubstrates, e.g., silicon wafers, are processed. The showerheadelectrode assembly 10 (only one-half of which is shown in FIG. 1)comprises a showerhead electrode including a top electrode 20 and anoptional backing member 40 secured to the top electrode 20, a thermalcontrol plate 58, and a top plate 80. The top plate 80 can form aremovable top wall of the plasma processing apparatus, such as a plasmaetch chamber.

A substrate support 15 (only a portion of which is shown in FIG. 1)including a bottom electrode and optional electrostatic clampingelectrode is positioned beneath the top electrode 20 in the vacuumprocessing chamber of the plasma processing apparatus. A substrate 16subjected to plasma processing is mechanically or electrostaticallyclamped on an upper support surface 17 of the substrate support 15.

The top electrode 20 of the showerhead electrode preferably includes aninner electrode member 22, and an optional outer electrode member 24.The inner electrode member 22 is preferably a cylindrical plate (e.g.,single crystal silicon). The inner electrode member 22 can have adiameter smaller than, equal to, or larger than a wafer to be processed,e.g., up to 12 inches (300 mm) if the plate is made of single crystalsilicon, which is the maximum diameter of currently available singlecrystal silicon material. For processing 300 mm wafers, the outerelectrode member 24 is provided to expand the diameter of the topelectrode 20 from about 15 inches to about 17 inches. The outerelectrode member 24 can be a continuous member (e.g., a poly-siliconmember, such as a ring), or a segmented member (e.g., 2-6 separatesegments arranged in a ring configuration, such as segments of singlecrystal silicon). In embodiments of the top electrode 20 that include amultiple-segment outer electrode member 24, the segments preferably haveedges which overlap each other to protect an underlying bonding materialfrom exposure to plasma. The inner electrode member 22 preferablyincludes multiple gas passages 23 for injecting a process gas into aspace in a plasma reaction chamber between the top electrode 20 andbottom electrode 15.

Single crystal silicon is a preferred material for plasma exposedsurfaces of the inner electrode member 22 and the outer electrode member24. High-purity, single crystal silicon minimizes contamination ofsubstrates during plasma processing as it introduces only a minimalamount of undesirable elements into the reaction chamber, and also wearssmoothly during plasma processing, thereby minimizing particles.Alternative materials that can be used for plasma-exposed surfaces ofthe top electrode 20 include SiC, SiN, AlN, and Al₂O₃, for example.

In a preferred embodiment, the showerhead electrode assembly 10 is largeenough for processing large substrates, such as semiconductor wafershaving a diameter of 300 mm. For 300 mm wafers, the top electrode 20 isat least 300 mm in diameter. However, the showerhead electrode assemblycan be sized to process other wafer sizes or substrates having anon-circular configuration.

The backing member 40 preferably includes a backing plate 42 and abacking ring 44. In such embodiments, the inner electrode member 22 isco-extensive with the backing plate 42, and the outer electrode member24 is co-extensive with the surrounding backing ring 44. However, thebacking plate 42 can extend beyond the inner electrode member such thata single backing plate can be used to support the inner electrode memberand the segmented outer electrode member. The inner electrode member 22and the outer electrode member 24 are preferably attached to the backingmember 40 by a bonding material, such as an elastomeric bondingmaterial. The backing plate 42 includes gas passages 43 aligned with thegas passages 23 in the inner electrode member 22 to provide gas flowinto the plasma processing chamber. The gas passages 43 can typicallyhave a diameter of about 0.04 inch, and the gas passages 23 cantypically have a diameter of about 0.025 inch.

The backing plate 42 and backing ring 44 are preferably made of amaterial that is chemically compatible with process gases used forprocessing semiconductor substrates in the plasma processing chamber,has a coefficient of thermal expansion closely matching that of theelectrode material, and/or is electrically and thermally conductive.Preferred materials that can be used to make the backing member 40include, but are not limited to, graphite and SiC.

The top electrode 20 can be attached to the backing plate 42 and backingring 44 with a thermally and electrically conductive elastomer bondingmaterial that accommodates thermal stresses, and transfers heat andelectrical energy between the top electrode 20 and the backing plate 42and backing ring 44. The use of elastomers for bonding together surfacesof an electrode assembly is described, for example, in commonly-ownedU.S. Pat. No. 6,073,577, which is incorporated herein by reference inits entirety.

The backing plate 42 and the backing ring 44 are preferably attached tothe thermal control plate 58 with suitable fasteners, which can bethreaded bolts, screws, or the like. For example, bolts (not shown) canbe inserted in holes in the thermal control plate 58 and screwed intothreaded openings in the backing member 40.

Referring to FIG. 1 and FIG. 2, the thermal control plate 58 comprises ametallic inner portion including a contoured plate 59 with an uppersurface 60, and a first projection 61 having an first heat transfersurface 62 and a second projection 63 having a second heat transfersurface 64 on the upper surface. In other preferred embodiments, thethermal control plate 58 can include more than two projections, e.g.,three or more projections. The thermal control plate 58 is attached tothe top plate 80 with fasteners that extend through oversized openings(not shown) in the top plate and into threaded openings 65 in thesurface 62 of the first projection 61 and surface 64 of the secondprojection 63 (FIG. 2). The thermal control plate 58 also includesthreaded openings 117 to receive fasteners to removably attach thethermal control plate 58 to the backing plate 42. The oversized openingsin the top plate 80 provide clearances around the fasteners so that thethermal control plate 58 can slide relative to the top plate toaccommodate mismatch in thermal expansion of the thermal control platerelative to the top plate.

The thermal control plate 58 also includes a flexure portion 66connecting the inner portion to an outer portion and including a flange68 having an upper surface 70 which is held against an opposed surfaceof top plate 80. The first heat transfer surface 62 and second heattransfer surface 64 preferably have an annular configuration. The firstprojection 61 and the second projection 63 preferably have a height offrom about 0.25 inch to about 0.75 inch, and a width of from about 0.75inch to about 1.25 inch. However, the first projection 61 and/or secondprojection 63 can have a non-annular configuration, e.g., arcuatesegment, polyhedral, round, oval or other configuration.

The thermal control plate 58 is preferably made of a metallic material,such as aluminum, an aluminum alloy, or the like. The thermal controlplate 58 is preferably a machined piece of the metallic material, suchas aluminum or aluminum alloy. The top plate 80 is preferably made ofaluminum or an aluminum alloy. The top plate 80 preferably includes oneor more flow passages 88 through which a temperature-controlled fluid,preferably a liquid, can be circulated to maintain the top plate at adesired temperature.

During processing of a semiconductor substrate in the processingchamber, heat is transferred from the inner electrode member 22 and theouter electrode member 24 and the backing plate 42 and backing ring 44to the lower surface 82 of the top plate 80 via thermal conduction fromthe first heat transfer surface 62, second heat transfer surface 64, andthrough upper surface 70. In other words, the first projection 61 andsecond projection 63 also provide thermal bridges between the innerelectrode member 22, outer electrode member 24, backing plate 42 andbacking ring 44 to the top plate 80. This enhanced heat transfer atspaced locations across the thermal control plate 58 can achieve asubstantially uniform temperature distribution radially across the topelectrode 20.

During operation of the showerhead electrode assembly 10, the thermalcontrol plate 58 and the top plate 80 become heated and thermallyexpand. As a result, the top plate 80 and thermal control plate 58 canslide relative to each other. This sliding can gall surfaces of the topplate 80 and/or thermal control plate 58 (e.g., one or more surfaces ofa central portion of the thermal control plate 58) that contact eachother and cause particles, such as aluminum particles, to be dislodgedfrom the contact surfaces. The loose particles may contaminatesubstrates in the reaction chamber and thereby reduce process yields.

It has been determined that galling of opposed surfaces of the top plate80 and/or the thermal control plate 58 can be minimized by placing amaterial that has lubricity between the opposed surfaces. In a preferredembodiment, at least one layer of a lubricating material 90 is placedbetween the first heat transfer surface 62 and the second heat transfersurface 64 of the thermal control plate 58 and the lower surface 82 ofthe top plate 80.

The lubricating material 90 has sufficient thermal and electricalconductivity to provide for sufficient heat transfer and electricalconduction from the first heat transfer surface 62 and second heattransfer surface 64 to the top plate 80. A preferred material thatprovides these properties is an elastically deformable graphitematerial, such as “GRAFOIL,” which is commercially available from UCARCarbon Co., Inc., Cleveland, Ohio. The lubricating material 90 ispreferably a gasket having a preferred thickness of about 0.010 inch toabout 0.030 inch, and more preferably about 0.015 inch. The lubricatingmaterial 90 is preferably a ring shaped gasket, with each gasket beingretained in a respective annular recess formed on each of the first heatsurface 62 and second heat transfer surface 64.

The lubricating material 90 is preferably protected from plasma exposurein the reaction chamber. In a preferred embodiment, the lubricatingmaterial 90 is disposed between vacuum seals, e.g., a pair of optionalO-rings 104 retained in spaced-apart annular grooves 105 in the firstheat transfer surface 62 and the second heat transfer surface 64 of thethermal control plate 58. The O-rings 104 isolate the lubricatingmaterial 90 from the vacuum environment in the plasma chamber andthereby protect the lubricating material from plasma exposure. The firstheat transfer surface 62 and the second heat transfer surface 64preferably are spaced from the lower surface 82 of the top plate 80 bythe lubricating material 90 by a sufficient distance so that there is nometal-to-metal sliding contact along the first heat transfer surface 62or the second heat transfer surface 64.

The thermal control plate 58 preferably includes at least one heateroperable to cooperate with the temperature-controlled top plate 80 tocontrol the temperature of the top electrode 20. For example, in apreferred embodiment, the heater is provided on the upper surface of thethermal control plate 58 and includes a first heater zone 72 surroundedby the first projection 61, a second heater zone 74 between the firstprojection 61 and the second projection 63, and a third heater zone 76between the second projection 63 and the flexure portion 66. The numberof heater zones can be varied; for example, in other embodiments theheater can include a single heater zone, two heater zones, or more thanthree heater zones. The heater can alternatively be provided on a bottomsurface of the thermal control plate 58.

The heater preferably comprises a laminate including a resistivelyheated material disposed between opposed layers of a polymeric materialthat can withstand the operating temperatures reached by the heater. Anexemplary polymeric material that can be used is a polyimide sold underthe trademark Kapton®, which is commercially available from E.I. du Pontde Nemours and Company. Alternatively, the heater can be a resistiveheater embedded in the thermal control plate (e.g., a heating element ina cast thermal control plate or a heating element located in a channelformed in the thermal control plate). Another embodiment of the heaterincludes a resistive heating element mounted on the upper and/or lowersurface of the thermal control plate. Heating of the thermal controlplate can be achieved via conduction and/or radiation.

The heater material can have any suitable pattern that provides forthermally uniform heating of the first heater zone 72, second heaterzone 74, and third heater zone 76. For example, the laminate heater canhave a regular or non-regular pattern of resistive heating lines such asa zig-zag, serpentine, or concentric pattern. By heating the thermalcontrol plate 58 with the heater, in cooperation with operation of thetemperature-controlled top plate 80, a desirable temperaturedistribution can be provided across the top electrode 20 duringoperation of the showerhead electrode assembly 10.

The heater sections located in the first heater zone 72, second heaterzone 74, and third heater zone 76 can be secured to the thermal controlplate 58 by any suitable technique, e.g., the application of heat andpressure, adhesive, fasteners, or the like.

In a preferred embodiment, the first heater zone 72, second heater zone74, and third heater zone 76 are electrically interconnected in seriesvia electrical connectors 77. In a preferred embodiment, the heatercomprises three circuits including a first resistive heated conductoradapted to receive AC current at a first phase, a second resistiveheated conductor adapted to receive AC current at a second phase, and athird resistive heated conductor adapted to receive AC current at athird phase, wherein the first, second and third phases are 120° out ofphase with each other.

As shown in FIG. 3, the heater can receive power from a single powersupply 110. In a preferred embodiment, the power supply 110 iselectrically connected to three circumferentially spaced posts, such asposts 95, received in openings 93 in the flange 68 of the thermalcontrol plate 58. The posts 95 are each connected to an electricalconductor 97, which extends through the flange 68 to a boot 79, andelectrically contacts a respective phase of the three-phase heaterlocated in the third heater zone 76. The three phases of the thirdheater 76 are electrically connected to the three corresponding phasesof the second heater via connections 77 and the three phases of thesecond heater are electrically connected to the three phases of thefirst heater by connections 77.

The thermal control plate 58 preferably includes lateral gas passages 75to allow process gas flow laterally from a plenum above the first heaterzone 72 to a plenum above the second heater zone 74, and from the plenumabove the second heater zone 74 to a plenum above the third heater zone76. In a preferred embodiment, a plurality of gas passages 75 extendthrough the first projection 61 and second projection 63. The gaspassages 75 are sized to allow the electrical connectors 77 to extendthrough the gas passages 75 to electrically connect the first heaterzone 72, second heater zone 74 and third heater zone 76. The gaspassages 75 are preferably large enough to allow the process gas to bedistributed over the upper surface of the thermal control plate 58 so asto provide a substantially uniform pressure distribution of gas passingthrough openings 78 communicating with plenums between the thermalcontrol plate and the backing member 40.

The top electrode 20 can be electrically grounded, or alternatively canbe powered, preferably by a radio-frequency (RF) current source. In apreferred embodiment, the top electrode 20 is grounded, and power at oneor more frequencies is applied to the bottom electrode to generateplasma in the plasma processing chamber. For example, the bottomelectrode can be powered at frequencies of 2 MHz and 27 MHz by twoindependently controlled radio frequency power sources. After asubstrate has been processed (e.g., a semiconductor substrate has beenplasma etched), the supply of power to the bottom electrode is shut offto terminate plasma generation. The processed substrate is removed fromthe plasma processing chamber, and another substrate is placed on thesubstrate support 15 for plasma processing. In a preferred embodiment,the heater is activated to heat the thermal control plate 58 and, inturn, the top electrode 20, when power to the bottom electrode is shutoff. As a result, the top electrode 20 temperature is preferablyprevented from decreasing below a desired minimum temperature. The topelectrode 20 temperature is preferably maintained at approximately aconstant temperature between successive substrate processing runs sothat substrates are processed more uniformly, thereby improving processyields. The power supply 110 preferably is controllable to supply powerat a desired level and rate to the heater based on the actualtemperature and the desired temperature of the top electrode 20.

The showerhead electrode assembly 10 can include one or more temperaturesensors, such as thermocouples, to monitor the top electrode 20temperature. The temperature sensors are preferably monitored by acontroller which controls supply of power from the power supply 110 tothe heater. When data provided by the temperature sensors indicates thatthe top electrode 20 temperature is below a predetermined temperature,the power supply 110 can be activated by the controller to supply powerto the heater so as to maintain the top electrode 20 at or above apredetermined temperature.

The heater can also be activated during plasma processing of substrates,i.e., when plasma is being generated between the showerhead electrodeassembly 10 and the bottom electrode. For example, during plasmaprocessing operations that utilize relatively low levels of appliedpower to generate a plasma, the heater can be activated to maintain thetemperature of the top electrode 20 within a desired temperature range.During other plasma processing operations that utilize relatively highpower levels, such as dielectric material etch processes, the topelectrode 20 temperature typically remains sufficiently high betweensuccessive runs so that the heater does not need to be activated toprevent the top electrode from falling below a minimum temperature.

In the embodiment shown in FIG. 3, the flexure portion 66 of the thermalcontrol plate 58 comprises a cylindrical wall extending to the flange68. The flange 68 is attached to the top plate 80, such as by fasteners(e.g., threaded bolts, screws, or the like) inserted into alignedopenings 84, 86 in the top plate 80 and flange 68, respectively (FIG.1). The flange 68 preferably has an annular configuration. The flexureportion 66 has a configuration that can accommodate thermal expansionand contraction of the thermal control plate 58 relative to the topplate 80. Namely, the flexure portion 66 preferably has a length tothickness ratio that is optimized to accommodate lateral and axialmovements between the central portions of the top plate 80 and thermalcontrol plate 58 and prevent associated damage to the thermal controlplate 58. During lateral sliding movement, the lubricating material 90prevents galling of the heat transfer surfaces 62 and 64 of the thermalcontrol plate 58, and the lower surface 82 of the top plate 80. Byproviding the flexure portion 66, a lubricating material can be omittedbetween the top surface 70 of the flange 68 and the lower surface 82 ofthe top plate 80.

The thermal control plate 58 is removably attached to the top plate 80with suitable fasteners, which extend through the openings 84 in the topplate 80 and into the openings 86 formed in the flange 68. In oneembodiment, the showerhead electrode assembly 10 comprises a cover plate120 attached to the top side 122 of the top plate 80. The cover plate120 seals the top ends of the openings in the top plate 80 such that thefasteners in these openings are at vacuum pressure in the processingapparatus. However, the cover plate can be omitted by providing a vacuumseal around the openings 86, (e.g., O-rings 104 can be provided aroundsections containing openings 86). In FIG. 2, three O-rings provide threevacuum sealed sections each of which contains six spaced-apart openings84.

In embodiments of the thermal control plate 58 in which the firstprojection 61 and second projection 63 each include O-rings 104 toprovide a vacuum sealed area between the thermal control plate 58 andthe top plate 80, the fasteners attaching the top plate 80 to thethermal control plate 58 can be exposed to atmospheric pressure in theprocessing apparatus if the tops of the bolts are not sealed.

A plurality of circumferentially-spaced alignment pins 106 areoptionally provided on the flange 68 of the thermal control plate 58.The alignment pins 106 are sized to fit in alignment openings (notshown) in the top plate 80 to circumferentially and radially align thethermal control plate 58 relative to the top plate 80.

The top plate 80 preferably includes one or more gas flow passages forintroducing process gas into one or more open spaces (plenums) betweenthe top plate 80 and the thermal control plate 58. For example, theprocess gas can be supplied only to the control plenum above the firstheater and distributed to the other plenums via passages 75. The processgas is flowed from the upper plenums through passages 78 to lowerplenums, and then through the gas passages 43 in the backing plate 42and the gas passages 23 in the inner electrode member 22. The gaspassages 78 are sized to provide a desired pressure drop through thethermal control plate 58. The gas passages 78 can typically have adiameter of about 0.3 inch. The number and arrangement of the gaspassages 78 is preferably selected to achieve uniform gas pressure aboveand across the top electrode 20 to provide uniform gas distribution intothe plasma chamber. The showerhead electrode assembly 10 can optionallyinclude baffles in the upper and/or lower plenums to control theuniformity of gas flow.

The temperature of the top plate 80 is preferably controlled by flowingheat transfer fluid (liquid or gas) through the flow passage(s) 88. Thetop plate 80 preferably provides an electrical ground, as well as a heatsink, for the showerhead electrode assembly 10.

As shown in FIG. 2, openings 114 are provided in the flange 68 of thethermal control plate 58 for passage of control rods of a plasmaconfinement assembly which can be provided outwardly of the showerheadelectrode assembly 10. A suitable plasma confinement assembly includinga vertically-adjustable, plasma confinement ring assembly is describedin commonly-owned U.S. Pat. No. 5,534,751, which is incorporated hereinby reference in its entirety.

While the invention has been described in detail with reference tospecific embodiments thereof, it will be apparent to those skilled inthe art that various changes and modifications can be made, andequivalents employed, without departing from the scope of the appendedclaims.

1. A thermal control plate for supporting a showerhead electrode in asemiconductor substrate processing chamber, comprising: a metal outerportion comprising an annular flange adapted to be removably attachableto a temperature-controlled top plate; and a metal inner portioncomprising a contoured plate, the inner portion including openings toreceive fasteners to removably attach the inner portion to theshowerhead electrode and the top plate, the inner portion providing athermal and electrical path between the top plate and showerheadelectrode; a metal flexure portion comprising a cylindrical wallextending from the annular flange to the inner portion and connectingthe outer portion to the inner portion, the flexure portion beingconfigured to accommodate differential thermal expansion between the topplate and the thermal control plate; and at least one heater on theinner portion operable to supply heat to the showerhead electrode. 2.The thermal control plate of claim 1, wherein the contoured platecomprises an upper surface and an annular first projection on the uppersurface, the first projection includes a first heat transfer surfaceadapted to transfer heat to the top plate, and spaced-apart annulargrooves configured to receive O-rings between the top plate and thefirst heat transfer surface.
 3. The thermal control plate of claim 2,wherein the contoured plate comprises an annular second projection onthe upper surface and radially spaced from the first projection, thesecond projection includes a second heat transfer surface adapted totransfer heat to the top plate, and optional spaced apart annulargrooves configured to receive O-rings between the top plate and thesecond heat transfer surface.
 4. The thermal control plate of claim 1,wherein the inner portion comprises at least one thermal bridgeproviding a thermal and electrical path between the top plate andshowerhead electrode.
 5. The thermal control plate of claim 1, whereinthe outer portion includes alignment pins adapted to fit in alignmentopenings in the top plate to provide circumferential and radialalignment between the thermal control plate and the top plate, threadedopenings adapted to receive bolts extending through a bottom side of thetop plate, and grooves adapted to receive O-rings between the top plateand the thermal control plate.
 6. The thermal control plate of claim 1,wherein the heater comprises an inner heater section in a central zoneof the contoured plate and at least one outer heater section disposedoutward from the central zone of the contoured plate, the inner heatersection and outer heater section being interconnected by at least oneelectrical connector.
 7. The thermal control plate of claim 1, whereinthe heater comprises a laminate including a resistive heating materialbetween dielectric layers.
 8. The thermal control plate of claim 1,wherein the heater comprises a three-phase heater.
 9. The thermalcontrol plate of claim 1, wherein the heater comprises three circuitsincluding a first resistive heated conductor adapted to receive ACcurrent at a first phase, a second resistive heated conductor adapted toreceive AC current at a second phase, and a third resistive heatedconductor adapted to receive AC current at a third phase, the first,second and third phases being 120° out of phase with each other.
 10. Thethermal control plate of claim 1, further comprising gas passagesextending between opposite sides of the inner portion.
 11. A thermalcontrol plate for supporting a showerhead electrode in a semiconductorsubstrate processing chamber, comprising: a metal outer portion adaptedto be removably attachable to a temperature-controlled top plate; and ametal inner portion connected to the outer portion by a metal flexureportion configured to accommodate differential thermal expansion betweenthe top plate and the thermal control plate, the inner portion includingopenings to receive fasteners to removably attach the inner portion tothe showerhead electrode and the top plate, the inner portion comprisingan upper surface and at least one projection on the upper surface, theprojection providing a thermal and electrical path between the top plateand showerhead electrode, wherein the outer portion, inner portion andflexure portion are a single piece of a metallic material.
 12. Thethermal control plate of claim 11, wherein the projection comprisesspaced-apart annular grooves configured to receive an O-ring between theprojection and the top plate.
 13. The thermal control plate of claim 11,wherein: the metal outer portion comprises an annular flange adapted tobe removably attachable to the temperature-controlled top plate; themetal inner portion comprises a contoured plate; and the metal flexureportion comprises a cylindrical wall extending from the annular flangeto the metal inner portion and connecting the outer portion to the innerportion.